In an automobile exhaust gas cleaning system, of the exhaust gas recirculation type, an exhaust gas recirculation valve (EGR valve) is used. The EGR valve recirculates a part of the exhaust gas from the exhaust system to the intake system in accordance with negative pressure in the carbureter.
An EGR valve is known which comprises a body which forms a passage connected to the exhaust line and another passage connected to the intake line, a valve member between said passages, and a diaphragm mechanism mounted on the body and having a diaphragm connected to the valve member through a rod so as to open or close the valve member in response to vacuum in the carbureter. In this known EGR valve, the diaphragm mechanism is of one of two types. One is a "single chamber type", which has a chamber formed on one side of the diaphragm apart from the body, and the other is a "double chamber type" which has a chamber formed on each side of the diaphragm.
In the known double chamber type, which is used when a complicated EGR operation is desired, the second chamber, formed on the side of the diaphragm facing the body, is formed so as to contact the surface of the body. In this case, to prevent leakage of the exhaust gas into the second chamber through a gap between the body and the rod which is in a slidable relationship with the body, a bellows member is used which is made of teflon material and is disposed between the rod and the body. The reason the teflon material is used is that temperature of the body through which the exhaust gas is recirculated becomes very high during the recirculation operation.
It should be noted that the teflon bellows can be used without thermal degradation when the temperature thereof does not exceed 270.degree. C. However, the temperature of the body is easily raised so as to exceed 270.degree. C., because the temperature of the exhaust gas is very high. Therefore, in the known EGR apparatus the EGR valve is used together with a cooling device for the exhaust gas (a so called EGR cooler) so as to prevent the bellows member from being thermaly degraded. Another drawback of the known EGR valve is that the manufacturing cost is relatively high because the teflon material is expensive.